1. Field of the Invention
The present invention relates to a radiation image capturing apparatus including a radiation detector for sensing a radiation image of a subject and outputting the radiation image as an electrical signal. More specifically, the present invention relates to a radiation image capturing apparatus including a cooling mechanism for cooling the radiation detector.
2. Description of the Related Art
In a radiation image capturing apparatus such as an X-ray breast image capturing apparatus (e.g., a mammography apparatus) or the like, a radiation image is generated by exposing a subject (patient) to radiation, and the radiation image is recorded into a radiation image recording unit (i.e., a radiation detector). Information corresponding to the radiation image is then read out by causing a reading light source to move relative to the radiation image recorder for applying a reading light. An example of such a radiation image capturing apparatus is disclosed in U.S. Pat. No. 6,268,614.
Examples of radiation image recording units that can be used in the aforementioned apparatus include a radiation detector of electric readout type having a plurality of photoelectric conversion elements and devices such as thin-film transistors (TFT), CCD (Charge Coupled Device) or CMOS (Complimentary Metal Oxide Semiconductor) sensor, along with light readout type, direct conversion type, or indirect conversion type radiation detectors.
In these types of radiation image capturing apparatus, a proper temperature range must be maintained due to constraints resulting from temperature characteristics of the photoelectric conversion elements, the effects of thermal noise generated in the electric circuits, and the like. Therefore, such radiation image capturing apparatus have been provided with an air cooler or a water cooler therein. One example of such an apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2000-037374.
Japanese Laid-Open Patent Publication No. 2000-037374 is directed to effective cooling of the radiation detector. As can be seen in FIG. 1 of the aforementioned publication, the radiation image capturing apparatus includes a two-dimensional radiation detector 5 and a signal converter 6, which are contained within a casing 4 of an image capturing unit 3, in this order from the front of the casing 4. A fan 7, which forms a cooling unit, is provided in an upper portion of the casing 4, and an inlet port 4a for introducing outside air is provided in a lower portion of the casing 4. Release of heat, which is generated by the two-dimensional radiation detector 5, can be carried out by actuating the fan 7, and thereby introducing air into the casing 4 through the inlet port 4a. 
In the apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-037374, the inlet port 4a is formed at one end of the radiation detector 5, while the fan 7 is located at the other end thereof, so that cooling of the entire radiation detector 5 can be achieved. In many types of radiation image capturing apparatuses, however, the arrangement of the radiation detector within the image capturing unit is restricted due to various reasons. In a mammography apparatus, for instance, it is necessary to capture images from various directions by moving the image capturing unit. The dimensions of the casing of the image capturing unit are therefore restricted, and the radiation detector has to be contained within a small space inside the casing. Moreover, because the mamographic image must include the base of the breast of the patient, the distance between the radiation detector and the chest wall of the patient has to be kept extremely short. Hence, in mammography apparatus, the radiation detector is located close to a side of the casing that abuts against the chest wall, thus making it difficult to release a sufficient amount of heat generated in the narrow space between the radiation detector and the side of the casing. This results in non-uniform cooling of the radiation detector, which in turn tends to cause imaging accuracy to deteriorate.